Iva Bartáková

Phytotoxicity of iron in relation to its solubility conditions and the effect of ionic strength

The effect of iron on root elongation and seed germination of Lactuca sativa was investigated within the limits of the plants sensitivity to an acidic environment and iron solubility under experimental conditions. Because ionic strength was found to have phytotoxic effects, the same pH and ionic strength conditions were kept constant over the entire iron concentration range, so as to evaluate solely the effect of iron. 0.14 mM Fe3+ was found to be the lowest effective concentration inhibiting root elongation. The low solubility of iron at a pH of 3 (the lowest value which could be applied for root elongation) excluded the testing of higher iron concentrations. Due to the lower sensitivity of seed germination to acidity, a pH of 2.6 could be applied in this case. The lowest effective iron concentration (the lowest applied concentration causing a significant decrease in germination as compared to the control, P < 0.05), EC50 (the concentration at which germination was 50% of that of the control specimens) and the completely effective iron concentration (the concentration that completely inhibited seed germination) were 0.6, 0.92 and 2.0 mM, respectively.

Pyrite biooxidation: Electrochemical and kinetic data

Studies on pyrite oxidation by Thiobacillus ferrooxidans , using a compact pyrite electrode, resulted in detection of 14 exchanged electrons. This indicates that the pyrite biooxidation to sulfate ions occurred at the pyrite surface without the formation of any sulfur intermediates. Exchange current density showed that the pyrite biooxidation rate was higher by one order of magnitude as compared to conditions without bacteria. Assuming sulfate is the final product, the initial rate of pyrite concentrate oxidation by ferric iron (up to 180 mM) was similar to the rate of pyrite concentrate oxidation by T. ferrooxidans in the absence of any significant ferric iron. Electrochemical and kinetic studies supported the indirect mechanism of pyrite oxidation based on iron-oxidizing activity of T. ferrooxidans .